A deal between the Organization of the Petroleum Exporting Countries and some non-OPEC producers to reduce output by 1.8 million barrels per day (bpd) in the first half of 2017 has had little impact on bulging global stockpiles of oil.

Brent crude, the international benchmark, fell 35 cents to $50.61 per barrel, heading back to its lowest level since OPEC announced on Nov. 30 its plan for cuts. The deal with non-OPEC states was reached in December.

U.S. light crude was down 35 cents at $47.89 a barrel, also heading back toward a three-month low.

"The lower the price goes, the higher the pressure on OPEC to extend cuts," Commerzbank analyst Carsten Fritsch said.

Sources have said OPEC is inclined to extend but wants backing from non-OPEC producers, including Russia, even though such countries have yet to deliver fully on existing cuts.

On Tuesday, the American Petroleum Institute reported U.S. inventories climbed by 4.5 million barrels to 533.6 million last week, a bigger rise than the 2.8 million analysts forecast.

Investors now want to see whether Wednesday's figures from the Energy Information Administration, a unit of the Department of Energy (DoE), confirm the rise.